Can't boot flash drive on GIGABYTE motherboard

Use Plop Boot Manager.

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Materials

2  computers
    1  computer with the problematic (GIGABYTE) motherboard
    1  computer for write operations to flash drives
2  USB FDDs
    1  (tiny capacity) flash drive for Plop Boot Manager
    1  (larger) flash drive for the anticipated boot disk
1  open USB slot

Setup

1. Download Plop Boot Manager. Get plpbt-x.x.x.zip (where x.x.x is the latest version number).
2. Extract the .zip file you downloaded.
3. In the folder resulting from the extraction, find plpbt.img.

4. Unmount your tiny FDD.

5. Write the file (Plop Boot Manager) to the beginning of your tiny FDD with this:

   Linux: sudo dd if=plpbt.img of=/dev/sdn

   Mac: sudo dd if=plpbt.img of=/dev/diskn

   (Assumes that you changed directories (cd plpbt-*) into the extracted folder. Replace the value of the of= parameter with the path of your particular flash drive. Be careful with this command by checking it for correctness!)

   Windows: Use Win32 Image Writer to write the .img file.

6. If you haven't already, write the bootable operating system to your other flash drive like normal.

Usage

1. Plug the Plop Boot Manager FDD into the computer with the problematic (GIGABYTE) motherboard.

   

2. Reboot or power on that computer. On GIGABYTE motherboards, press F12 at the BIOS splash.

   

3. Select the Plop Boot Manager FDD for booting. On GIGABYTE motherboards, choose either USB-ZIP or USB-HDD. The flash drive is actually recognized as a floppy, not a regular flash drive.

   

4. Plop Boot Manager should now be running. There may be a starfield screensaver in the background.
5. Plug in the other FDD. (Exchange with the Plop Boot Manager FDD if you're out of slots.)

6. Select the flash drive option from the Plop Boot Manager menu.

   

Now the bootable flash drive operating system should be starting up!

As a bonus, there are other uses for your Plop Boot Manager FDD now, and it can be your "key" to other possible booting issues you might encounter.

1. In the BIOS, ensure you have Integrated Peripherals > USB Legacy Enabled.
2. Also ensure you have Integrated Peripherals > USB Storage Enabled.
3. Set Boot Order to HDD, None, None.
4. With the USB Boot Drive inserted, Reboot.
5. Hit F12 at the Boot Screen to bring up the Boot Menu.
6. Choose HDD+ on the Boot Screen, not any of the USB options!
7. Choose your USB Device on the next screen.

Source: http://forums.tweaktown.com/gigabyte/24883-welcome-gigabyte-technical-support-133.html#post394471

HOURS of research - I hope this helps.